The long-term objectives of this research is to unravel the role of oligodendrocytes (OLG) in multiple sclerosis and to understand the biology of OLG as myelin forming and myelin maintaining cells. In previous work we have shown that the plasma membrane (PM) of mature OLG has a protein profile that is distinct from myelin. We have also shown that a highly purified fraction of OLG-PM can be further resolved by density equilibrium centrifugation on a linear sucrose gradient into three fractions, F2.2a, F2.2b, B2.2c and a pellet, F2.2p. Circumstantial evidence suggests that these fractions may be structural (and functional?) PM domains. However, because these fractions were isolated from OLG that have been in culture for 5 days in a non-attached state we believe that randomization might have occurred. The work proposed has two major objectives. The first one is to define the OLG- PM/myelin compartments by: a) elucidating the mechanism(s) of translocation of myelin components from OLG into myelin; b) confirming if OLG PM is composed of PM domains. For this we will purify the PM of OLG that have been attached to a substratum (i.e., polarized cells) both shortly after attachment and after long-term culture and c) undertaking the chemical characterization of OLG-PM. These studies should yield new information on OLG-PM; they should prove/disprove the postulate that OLG-PM has membrane domains and they should open a way of distinguishing between proteins that pertain to cellular functions from those relevant for myelination. Our second objective is to investigate the biological consequences of adding neurons to OLG cultures. Having observed that OLG can assemble myelin in the absence of neurons (myelin palingenesis), we propose to examine if neurons make a difference. Thus, we will study the effect of neurons on the expression of myelin palingenesis and remyelination. Finally, we will study the role of proteoglycans and glycoproteins secreted by OLG to the medium or purified from myelin on the growth of neuronal cultures and on OLG-neuron interaction. This research should provide insight into the nature of OLG-neuron interaction and on the factors that influence it.